B. Eating a variety of healthy food.
It's not A because the body needs more than just protein. It can't be C because even though juice might have vitamins (and a LOT of sugar), it might not have pulp from the fruit that it is made out of. Pulp gives you fiber. It cannot be D because even if you don't eat anything fatty, some fats are actually necessary for your body. It's got to be B.
